In conventional furnaces for the melting of metal or for the treatment of molten metal, the furnace roof is typically either lined with a refractory material or is constructed of steel panels with enclosed, circulating cooling water systems embedded therein. In the latter, the cooling water is circulated at high volume and under pressure.
Examples of some typical prior art systems are described in U.S. Pat. Nos. 205,274 (1878), 1,840,247, 4,015,068, 4,107,449, 4,132,852, 4,197,422, 4,216,348, 4,273,949, 4,345,332, 4,375,449, 4,410,996, 4,411,311, 4,423,513, 4,425,656 and 4,449,221; German patent specification Nos. 30 27 465.8-24 and 1 108 372; and Japanese patent application publications 57-48615 and 45-29728.
The structure in U.S. Pat. No. 4,410,996 employs side-wall refractories as well as a suspended refractory roof in which the suspension members are water cooled pipes. The only spray cooling disclosed in this patent is at the side wall gas exhaust ducts 11a and 11b, and the spray is intended to cool the gasses exiting the ducts.
The patents to NORTHRUP U.S. Pat. No. (1,840,247) and KELLER, et al U.S. Pat. No. (4,449,221) both disclose furnaces in which sprays of cooling water are directed against metal plates in the side walls of the furnace to cool refractory material carried by the plates and prolong the life of the refractory material.
The patent to SOSONKIN et al U.S. Pat. No. (4,107,449) discloses a furnace in which refractory material lines the roof and side wall, and in which water is circulated through distinct roof panels or sections to cool the roof. In FIG. 7, a part of the water supply system is shown and in column six, lines 5 through 8, pipes 27 with holes 28 are described as directing streams of water onto the roof panels. There is no disclosure of a spray. It is believed that cooling of the roof in this patent is accomplished by flooding the surface to be cooled.
U.S. Pat. Nos. 205,274 and 4,411,311 both disclose blast furnace cooling systems in which discrete sections are provided in the side walls of the furnace with water circulated therethrough to cool the refractory material.
U.S. Pat. Nos. 4,015,068 and 4,375,449 both describe arrangements in which cooling water is caused to flow over the outer surface of furnaces.
The remaining patents disclose systems in which the cooling water is circulated in closed systems through pipes, panels, etc. In these systems, the cooling water is circulated in large volumes under high pressures. These systems must be carefully maintained and operated since any blockage of coolant water flow can result in flashing of the water to stream, causing a sudden and dangerous increase in pressure which may cause failure of the roof and an explosion when the water flows into the molten metal. Similar consequences may follow in the event of a leak developing in the cooling system, particularly in view of the large volumes of water and high pressures in the cooling systems.